Basic Network Concepts
In this appendix I briefly review some basic ideas in network analysis of social relationships, including core concepts and principles, data collection procedures, and methods of analysis. I provide brief substantive illustrations of these ideas, using research examples from both the individual and organizational levels of analysis. This nontechnical introduction should provide readers with sufficient vocabulary to understand the network structures and processes discussed in this volume. For extensive technical and substantive reviews of network analysis, consult Knoke and Kuklinski (1982), Burt and Minor (1983), Mizruchi (1994), Brass (1995), Wasserman and Galaskiewicz (1994), and Wasserman and Faust (1994). This appendix is a revision of portions appearing in Knoke (1999).
and System Boundaries
Networks are social constructions arising from the continual exchanges and joint activities among participants in a social system, defined as a "plurality of actors interacting on the basis of a shared symbol system" (Parsons 1951:19). The recurrent pattern of relations connecting the actors constitutes that system's social structure. The actors belonging to a network may be designated at varying levels of analysis: individuals (children in a kindergarten class); small groups (work teams on an automobile assembly line); formal organizations (corporations in a business association); coalitions (lobbying alliances); even nations (members of the World Trade Organization). More complex network structures may bring together actors from multiple levels of analysis, for example, connecting individual patients, nurses, and physicians with the emergency room, maternity ward, laboratory, and housekeeping units of a community hospital.
Identifying the boundaries of a social system, and hence its size, requires the researcher to specify which potential members must be considered relevant or irrelevant to the social system's functioning. An investigator using a nominalist strategy typically achieves conceptual closure by including all actors that possess one or more key characteristics (Laumann, Marsden and Prensky 1983). Nominal designations often restrict network membership to incumbents occupying formal positions, for example, to directors of the Fortune 500 companies or middle managers at Apple Computer. Involvement in particular activities may also define the boundary, as in Laumann and Knoke's (1987:97-98) stipulation that the U.S. energy or health